The K01 award will facilitate the mentored transition of Dr. Rossana Occhipinti from a postdoctoral position to an independent investigator, capable of combining in-silico (i.e., using computer) and in-vitro experiments in the field of multi-scale modeling of kidney acid-base physiology. Dr. Occhipinti is an applied mathematician with expertise in mathematical modeling of complex biological systems and acid-base physiology. Her postdoctoral training has been in the wet-laboratory of her primary mentor, Professor Walter Boron. Here, her research has focused on developing sophisticated mathematical models to simulate the data on intracellular pH (pHi) and extracellular-surface pH obtained in the laboratory from electrophysiology experiments. However, because Dr. Occhipinti's research has focused only on mathematical modeling and her career goals depend on having expertise in two distinct but complementary areas, it is critical that, in addition to perform state-of-art modeling she acquires the knowledge and ability to perform sound in-vitro experiments to inform her in-silico experiments. This K01 award will provide Dr. Occhipinti with the necessary protected amount of time to obtain appropriate training in electrophysiology, proximal tubule (PT) perfusion, and optics while continuing to expand her mathematical modeling expertise. Dr. Occhipinti's career development plan includes focused coursework, mentorship from a multi-disciplinary group of leading investigators, and practical research experience focusing on training in: (1) molecular biology, transport/electrophysiology, and oocyte experiments (Aim 1); (2) renal physiology and proximal- tubule perfusion/optical imaging (Aim 2); and (3) sophisticated mathematical modeling (Aim 3). Moreover, Dr. Occhipinti will engage in professional development and networking activities. The research plan focuses on the unknown key question of how proximal-tubule cells can reconcile the competing demand of two vital processes: H+ secretion versus regulation of their own pHi. To answer this question, the research plan has 3 aims that will assess key properties of the major acid-base transporters in PTs: (1) the electrogenic Na/HCO3 cotransporter (NBCe1-A) at the basolateral membrane (BLM), (2) the Na-H exchanger 1 (NHE1) at the BLM, and (3) the NHE3 at the apical membrane. In Aim 1, Dr. Occhipinti will determine for the first time the pHi dependence of NBCe1-A as heterologously expressed in oocytes. In Aim 2, she will assess the roles of NHE1, NHE3 and NBCe1-A from pHi recording on intact PTs. In Aim 3 she will use the results from Aim 1 and Aim 2 to create and inform a comprehensive and novel mathematical model of acid-base transport and pHi regulation for a PT cell. By pursuing these specific aims, Dr. Occhipinti will develop the knowledge and skills to perform electrophysiology and optical experiments that will (1) allow her to be independent of other laboratories in gathering the data needed to test and validate her mathematical models, and (2) prepare her to write her first R01 application. Dr Occhipinti life's work should inform our understanding of the many clinical conditions that challenge or interfere with the ability of the kidney to handle acid loads, and should be applicable in a general sense to a wide range of other epithelia.